Spark plug



Feb. 24, 1931. R. T. HURLEY ET AL SPARK PLUG Filed' April 4, 1927 Planted Feb. 24, 1931 I UNITED STATES PATENT OFFICE ROY T. HURLEY, or DOBBS FERRY, AND GEORGE E. PaULsON', or ASTORIA, NEW YORK, ASSIGNORS TO THE B. G. CORPORATION, A CORPORATION OF NEW YORK sRARK PLUG Application filed April 4, 1927. Serial No. 180,779.

This invention relates to spark plugs and has for an object a midget or small-sized spark plug of great durability for use where space is at a premium and where soft insulation material such as mica is used, as in aeroplane engines, and one capable of withstanding the high temperatures and. pressures in such engines.

Other objects, novel features and advan- 1 tages of the invention will be apparent from the following specification and accompanying drawings wherein Figure 1 is a cross-section of a spark plug embodying my invention;

l the mode of assembly;

Fig. 3 is a similar view of Fig. .2, showing the plug as assembled;

Fig. 1 is a detail section showing a mod-- ified form of sealing ring; and

Fig. 5 is a view of same prior to assembly. 10 is a spindle at the lower end of which is provideda head 11 in which is mounted an electrode '12. A sleeve 13 of insulating mate rial, such as a mica sheath, surrounds the spindle 10 and has one end abutting the head 11. minates short of the end of the spindle and a terminal cap 14 surrounds the projecting end of the spindle 10. Surrounding the lower end of the sleeve 13 and resting on the head 11 is an inverted conical member 15 of insulating material. A sealing member 16 of general conical configuration and having a base 17 rests upon the member 15 and surrounds the sleeve 13. The member 16 is composed of some compressible material such, for example, as a soft metal like brass. A bushing 18 fits over the member 16 and is exteriorly threaded. A truncated cone 19 of insulating material surrounds the sleeve 13 and is interposed betweenthe plug 18 and the terminal 14. The bushing 18 screws into the body 20 of the plug which is provided with threads 21 by means of which it may be screwed into a suitable socket in an engine. The upperend of the spindle 10 is headed over as at 22 to bind together the various elements forming the spark plug. 50 As this spark plug is of the midget t'ype,

Fig. 2 is a detail section showing a step in The other end of the sleeve ter-.

of the bushing 18, its sharp edge projects The slightly into the cylindrical portion of the bore, and as a result the edge is turned outwardly as shown in the drawing. This pre vents the sharp edge of the sealing cone from tearing the sleeve 13 and prevents the concentration of electrical stresses along a line which would cause electrical leakage through the thin sleeve. It is thus possible to obtain a gas-tight seal and complete electrical insulation in a midget-sized plug where the construction of such plug involves a small diameter spindle and the use of a corresponding sheath of thinly-split mica.

Between the conical portion of the sealing member and its base 17, there is provided a gap. This gap permits the making of the conical portion of the sealing ring less tapering as well as permitting the member 16 to compress uniformly under less pressure than otherwise and also permits the base 17 to remain perpendicular to the spindle 10 as a firm support for the member 15. The construction .of the sealing ring 16 in wedge shape and having a base divided therefrom by'a partial gap has the advantage of causing part 0 the cone with a tendency to cause the inner face of the sealing ring to bulge slightly, thus forming a perfect gas-tight joint. Furthermore, it is desirable, as shown in the drawings, that the bushing at its end next to member 19 have a bore of slightly larger diameter than the cone., Thus, as the conical edge of the sealing ring is forced into place, the pointed edge tends to flare outwardly and away from the mica sheath.

After the various elements have been assembled on the spindle 10 and'the terminal 14 put in place, the top of the spindle is the stresses to be placed along the mid part of thin end extending into ing said spindle,

headed over to lock these elements in assembled position. In order to expedite this riveting operation, the spindle 10 is originally provided with a shallow hole at its upper end, the spindle being slightly longer than it is in'its finished condition. By means of a riveting machine, the edges of the hole are flared over the terminal 14, thus completing the assembly of the core.

The construction above described provides a gas-tight seal and complete electric insula-' tion. Because of the shape and larger diameter of the bore of the bushing 18, the sharp edge of the sealing member 16 is turned outwardly, thereby perventing its digging into the sleeve 13. The mechanical' strains and electrical stresses are uniformly distributed over a large area which is highly desirable in such a small spark plug.

A modified form of sealing ring is shown in Figs. 4 and 5. In this modification, the sealing ring is not made of conical shape, but is cylindrical in form. It is provided, however, before assembly with an outward bulge 23. In this case, the bushing is provided with a straight cylindrical bore. As the modified sealing ring is forced into place, being of compressible material, the outward bulge 23 is transformed by compression through the bushing into an inward bulge 24, as shown in Fig. 4, thus forming an air-tight sealing joint around the inica sheath and around the spindle. Such modified form of sealing ring is preferably provided with a fiat head 25 as in the case of the conical ring.

It is understood, of course, that various changes may be made in the structure of the elements comprising the spark plug above described without in any way the spirit of the invention as set forth in the appended claims.

We claim:

1. In a spark plug, a central metallic spindle, a sleeve of insulating material surrounding said spindle, a bushing surrounding said sleeve, the bore of said bushing being-partially frusto-conical partially cylindrical, cal, and a frusto-conical sealing member wedged between said sleeve and bushing, said sealing member being of soft metal and hav ing its thin end projecting into the cylindrical portion of said bore.

2. In a spark plug, a central metallic spindle, a sleeve of insulating material surrounda bushing surrounding said sleeve, the bore of said bushing being partially frust-conical partially cylindrical,

and a sealing member wedged between said sleeve and bushing, said sealing member comprising a frusto-conical portion having its the cylindrical part of said bore and a cylindrical base, a partial gap between said base and said frusto-conical portion, and a member carried by said spindle against which said base abuts.

3. In a spark plug, a central metallic spindle, an insulating sheath surrounding said spindle, a bushing surrounding said sheath, and a conical soft compressible sealing ring wedged between said plug and said sheath and having its pointed edge outwardly flared.

4. In a spark plug, a central metallic spindle, a sleeve of insulating material surrounding said spindle, a bushing surrounding said sleeve and a sealing member, wedged between said sleeve and said bushing, the shape of said bushing and said sealing member providing a bulgeon said sealing member to form a gas-tight joint between said sleeve and said spindle.

5. In a spark plug, a central metallic spindle, a sleeveof insulating material surrounding saidspindle, a bushing having a cylindrical bore surrounding said sleeve, and a sealing member of soft metal provided with a bulge wedged between said sleeve and said bushing.

6. In a spark plug a central metallic spindle, a sleeve of insulating material surrounding said spindle, a bushing surrounding said sleeve and a sealing member of soft metal wedged between said sleeve and said bushing, said wedge and bushing being so shaped as to cause a portion of the inner surface of said wedge to bulge into said sleeve.

In testimony whereof, we have signed our names to this specification.

ROY T. HURLEY. GEORGE M. PAULSON.

departing from of soft metal 

